550 research outputs found
Inelastic Diffraction at Heavy Ion Colliders
The heavy ion physics approach to global event characterization has led us to
instrument the forward region in the PHENIX experiment at RHIC. In heavy ion
collisions this coverage yields a measurement of the "spectator" energy and its
distribution about the beam direction. This energy flow is the basis of
event-by-event determination of the centrality and reaction plane which are key
to analyzing particle production in heavy ion collisions. These same tools have
also enabled a unique set of measurements on inelastic diffraction with proton,
deuteron and gold ion beams in the PHENIX experiment. We present first new
results on this topic and discuss briefly the opportunity for diffractive
physics with Heavy Ion beams at the LHC.Comment: RHIC overview talk presented at "Diffraction 2004" in Dorgali,
Sardegna, Ital
Source Parameters from Identified Hadron Spectra and HBT Radii for Au-Au Collisions at sqrt(s_NN)=200 GeV in PHENIX
The characteristics of the particle emitting source are deduced from low
transverse momentum identified hadron spectra (transverse mass less than 1 GeV)
and HBT radii using a hydrodynamic interpretation. From the most peripheral to
the most central data, the single particle spectra are fit simultaneously for
all pions, kaons, and (anti-)protons using the parameterization in [1] and
assuming a linear transverse flow profile. Within the systematic uncertainties,
the expansion parameters called the freeze-out temperature and flow velocity,
respectively decrease and increase with the number of participants, saturating
for both at mid-centrality. The expansion using analytic calculations of the kT
dependence of HBT radii in [2] is fit to the data but no chi-squared minimum is
found.Comment: 4 pages, 4 figures, Contribution to Quark Matter 2002, Nantes,
France, July 18-24, 2002. To appear in the proceedings (Nucl. Phys. A
Transport model analysis of particle correlations in relativistic heavy ion collisions at femtometer scales
The pion source as seen through HBT correlations at RHIC energies is
investigated within the UrQMD approach. We find that the calculated transverse
momentum, centrality, and system size dependence of the Pratt-HBT radii
and are reasonably well in line with experimental data. The predicted
values in central heavy ion collisions are larger as compared to
experimental data. The corresponding quantity of the
pion emission source is somewhat larger than experimental estimates.Comment: 12 pages, 5 figures, to be published in PR
Event-by-event study of DCC-like fluctuation in ultra-relativistic nuclear collisions
A method based on sliding window scheme is developed to search for patches in
the pseudorapidity-azimuth plane, on an event-by-event basis, having unusual
fluctuation in the neutral pion fraction which may arise due to the formation
of Disoriented Chrial Condensates (DCC) in high energy nuclear collisions. The
efficiency of the method to extract the patches and the purity of the extracted
sample are studied for possible experimental situations.Comment: 10 pages, 5 figure
Is Anomalous Production of Omega and anti-Omega Evidence for Disoriented Chiral Condensates?
No conventional picture of nucleus-nucleus collisions has yet been able to
explain the abundance of Omega and anti-Omega hyperons in central collisions
between Pb nuclei at 158 A GeV at the CERN SPS. We argue that this is evidence
that they are produced as topological defects arising from the formation of
disoriented chiral condensates (DCC) with an average domain size of about 2 fm.Comment: version 2 containing formulas, accepted by PR
Evolution of Fluctuation in relativistic heavy-ion collisions
We have studied the time evolution of the fluctuations in the net baryon
number for different initial conditions and space time evolution scenarios. We
observe that the fluctuations at the freeze-out depend crucially on the
equation of state (EOS) of the system and for realistic EOS the initial
fluctuation is substantially dissipated at the freeze-out stage. At SPS
energies the fluctuations in net baryon number at the freeze-out stage for
quark gluon plasma and hadronic initial state is close to the Poissonian noise
for ideal as well as for EOS obtained by including heavier hadronic degrees of
freedom. For EOS obtained from the parametrization of lattice QCD results the
fluctuation is larger than Poissonian noise. It is also observed that at RHIC
energies the fluctuations at the freeze-out point deviates from the Poissonian
noise for ideal as well as realistic equation of state, indicating presence of
dynamical fluctuations.Comment: 9 pages and 6 figures (Major modifications done
Heavy ion collisions: Correlations and Fluctuations in particle production
Correlations and fluctuations (the latter are directly related to the
2-particle correlations) is one of the important directions in analysis of
heavy ion collisions. At the current stage of RHIC exploration, when the
details matter, basically any physics question is addressed with help of
correlation techniques. In this talk I start with a general introduction to the
correlation and fluctuation formalism and discuss weak and strong sides of
different type of observables. In more detail, I discuss the two-particle
correlations/\mpt fluctuations. In spite of not observing any dramatic
changes in the event-by-event fluctuations with energy, which would indicate a
possible phase transition, such correlations measurements remain an interesting
and important subject, bringing valuable information. Lastly, I show how radial
flow can generate characteristic azimuthal, transverse momentum and rapidity
correlations, which could qualitatively explain many of recently observed
phenomena in nuclear collisions.Comment: 8 pages, 8 figures. Invited talk at 5th International Conference on
Physics and Astrophysics of Quark Gluon Plasma, February 8-12, 2005, Salt
Lake City, Kolkata, Indi
A Unified Approach towards Describing Rapidity and Transverse Momentum Distributions in Thermal Freeze-Out Model
We have attempted to describe the rapidity and transverse momentum spectra,
simultaneously, of the hadrons produced in the Ultra-relativistic Nuclear
Collisions. This we have tried to achieve in a single statistical thermal
freeze-out model using single set of parameters. We assume the formation of a
hadronic gas in thermo-chemical equilibrium at the freeze-out. The model
incorporates a longitudinal as well as a transverse hydrodynamic flow. We have
also found that the role of heavier hadronic resonance decay is important in
explaining the particle spectra.Comment: 22 pages, 11 figure
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